Well completion in friable sands

ABSTRACT

This specification discloses a well completion system for use in unconsolidated formations and a process for producing fluids from wells penetrating such formations. A well is provided that extends into the unconsolidated formation and has an open production interval that communicates with the formation. A sand retainer is installed adjacent a lower portion of the open production interval. The sand retainer extends from the lower extremity of the open production interval upward to an intermediate location of the open production interval. Fluids are produced from the well at a rate such that sand arches are formed and the formation is stabilized, thus permitting a high rate of production of hydrocarbons with a minimum production of sand from that portion of the unconsolidated formation above the sand retainer. Concomitantly therewith fluids are produced from the formation through the sand retainer, which sand retainer controls the flow of sand from the portion of the formation adjacent the sand retainer.

United States Patent [191 Stein et al.

I I I 3,756,3i8

14 1 Sept. 4, 1973 WELL COMPLETION IN FRlABLE SANDS [75] Inventors:Nathan Stein; Lloyd G. Jones, both of Dallas, Tex.

[73] Assignee: Mobil Oil Corporation,New York,

[22] Filed: June 30, 1971 [21] Appl. No.: 158,332

[52] US. Cl. 166/278 [51] Int. Cl. E2lb 43/04 [58] Field of Search166/278, 314, 276

[56] References Cited UNITED STATES PATENTS 2,434,239 l/l948 Zublin166/278 Primary Examiner-Robert L. Wolfe v Attorney-William .I.Scherback, Henry H. Ehrlich et al.

[57] ABSTRACT This specification discloses a well completion system foruse in unconsolidated formations and a process for producing fluids fromwells penetrating such formations. A well is provided that extends intothe unconsolidated formation and has an open production interval thatcommunicates with the formation. A sand retainer is installed adjacent alower portion of the open production interval. The sand retainer extendsfrom the lower extremity of the open production interval upward to anintermediate location of the open production interval. Fluids areproduced from the well at a rate such that sand arches are formed andthe formation is stabilized, thus permitting a high rate of productionof hydrocarbons with a minimum production of sand from that portion ofthe unconsolidated formation above the sand retainer. concomitantlytherewith fluids are produced from the formation through the sandretainer, which sand retainer controls the flow of sand from the portionof the formation adjacent the sand retainer.

12 Claims, 1 Drawing Figure PATENTEDSEP 4 ms 3. 7 56.318

NATHAN STEIN LLOYD G. JONES INVENTORS ATTORNEY WELL COMPLETION INFRIABLE SANDS BACKGROUND OF THE INVENTION This invention relates to theproduction of fluids from subterranean formations and more particularlyto well completion systems for use in unconsolidated formations and toprocesses for producing fluids from wells penetrating such formations.

In the production of hydrocarbons from hydrocarbon-bearingunconsolidated formations, a well is provided which extends from thesurface of the earth into the unconsolidated formation. The wellnormally terminates within the formation above the location of anybottom water which may underlie the hydrocarbons in the formation. Thewell may be completed by employing conventional completion practices,such as running and cementing casing in the well and formingperforations through the casing and cement sheath surrounding thecasing, thereby forming an open production interval which communicateswith the formation.

The production of hydrocarbons from unconsolidated formations may resultin the production of sand along with the hydrocarbons. Produced said isundesirable for many reasons. It is abrasive to components within thewell, such as tubing, pumps and valves, and must be removed from theproduced fluids at the sur face. Further, it may partially or completelyclog the well, thereby making necessary an expensive workover. Inaddition, the sand flowing from the formation may leave therein a cavitywhich may result in caving the formation and collapse of the casing.

A technique commonly employed for controlling the flow of sand from anunconsolidated formation into a well involves the forming of a gravelpack in the well adjacent the entire portion of the unconsolidatedformation exposed to the well. Thereafter, hydrocarbons are producedfrom the formation through the gravel pack and into the well. Gravelpacks have generally been successful in mitigating the flow of sand fromthe formation into the well. However, the flowing of fluids through thegravel pack results in a pressure drop across the gravel pack. Thispressure drop results in loss of energy from the formation, therebyreducing the total amount of and rate at which the hydrocarbons may beproduced from the formation into the well.

SUMMARY OF THE INVENTION In accordance with this invention there isprovided a well completion system for use in a well penetrating anunconsolidated formation of the earth. In a well having an openproduction interval in an unconsolidated formation there is provided asand retainer that is located adjacent a lower portion of the openproduction interval which said retainer terminates at its upperextremity at an intermediate location of the open production interval.

In a further aspect of this invention there is provided a method ofproducing a well which utilizes the abovedescribed system. In carryingout this method, fluids are produced through the sand retainer.Concomitantly therewith fluids are produced from the formation into thewell through an upper portion of the open production interval above thesand retainer.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic view,partially in cross section, of a well completed in an unconsolidatedsubsurface formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention is directed towell completion systems for use in unconsolidated formations and toprocess for producing fluids from wells penetrating such formations.This invention enables the mitigation of two of the major problems whichoccur in the production of hydrocarbons from unconsolidated formations.One of these problems concerns the reduced production rate from theformation which results from the use of a gravel pack to control theflow of sand from the formation. The other problem concerns the damageto the formation which results from water-coning.

With reference to the drawing, there is illustrated a well 1 whichextends from the surface of the earth 3 into an unconsolidated formation5 having a hydrocarbon-bearing portion 6 and a bottom water portion 7.The well I normally terminates above the upper level of botom water 7.Well 1 is equipped with casing 9 that is bonded to the walls of the wellby cement sheath 1 l. Perforations 13 extend through casing 9 and cementsheath 1], thereby forming an open production interval 12 that providesfor fluid communication between the interior of well 1 andunconsolidated formation 5. Production tubing 27, extending from thesurface of the earth to the wellbore bottom, and communicating throughopenings 26 with the interior of well 1, may be provided fortransporting fluids from well 1 upward to the surface of the earth. Theequipment thus described for completing well 1 is conventional and othersuitable completion systems may be employed.

In accordance with the present invention there is provided a wellcompletion system for use in a well penetrating an unconsolidatedformation of the earth. The well 1 penetrates the unconsolidatedformation 5 and normally terminates above bottom water 7. There areprovided perforations 13 through the casing 9 and cement sheath 11,thereby forming an open production interval 12 which communicates withthe unconsolidated formation 5. A sand retainer 15 is provided in a well1 adjacent a lower portion of the open production interval 12. The sandretainer 15 extends upward from the lower extremtiy of open productioninterval 12 to an intermediate location thereof.

Preferably, the sand retainer 15 is a gravel pack. Gravel packs andtechniques of placing them in wells are readily available at economiccost in the oil industry. The gravel pack may take the form illustratedin the drawing wherein it is formed intermediate production tubing 27and casing 9 and held in place by hold down packer 23. In suchcompletion, a packer 25 is normally set intermediate production tubing27 and casing 9 at about the upper location of unconsolidated formation5 to ensure that fluids produced from unconsolidated formation 5 flowinto the open portion of production tubing 27. Other types of gravelpacks may be employed. For example, a gravel pack may be placed outsideof casing 9 immediately adjacent unconsolidated formation 5. Also,consolidated gravel packs may be employed. A service for forming aconsolidated gravel pack is available under the trade name of Conpac.Other means than gravel packs may be employed as sand retainer 15. Forexample, an epoxy resin may be injected into the formation toconsolidate the formation and thereby control the sand productiontherefrom. A service whereby a resin is employed for controllingunconsolidated formation sands is available under the trade name ofEposand. Both Conpac and Eposand are offered by I-Ialliburton Services,Inc., and are described on page 2422, Vol. 2, 29th Revision of theCOMPOSITE CATALOG OF OIL FIELD AND SERVICES, WORLD OIL, 1970-1 97 1.Also, mechanical said retainer means, such as screens and slotted pipes,may be employed.

In accordance with a preferred embodiment of this invention, the sandretainer 15 terminates at approximately the uppermost location 21 towhich a water cone 17 will rise from bottom water 7 when the well 1 isproduced at a predetermined production rate for a specified time. Thus,the production of sand from the zone of the unconsolidated formationthat is invaded by water cone 17 is controlled by sand retainer 15.Preferably, the sand retainer is located adjacent no more than the lower75 percent of the open production interval 12. This allows the maximumproduction rate of fluids to be realized from at least the uppermost 25percent of the open production interval 12 while controlling theproduction of sand from the zone of the unconsolidated formation 5invaded by water cone 17. This also allows water to be produced from thewater cone 17 through the sand retainer 15 and thereby to limit theupward extension of water cone 17.

In accordance with another aspect of this invention, fluids are producedfrom the unconsolidated formation 5 through the sand retainer 15 andinto well 1. Concomitantly therewith fluids are produced from theunconsolidated formation 5 into well 1 through an upper portion of theopen production interval 12 above the sand retainer 15. The fluids areproduced from the unconsolidated formation 5 at a rate such that sandarches are formed and the formation is stabilized adjacent the openproduction interval 12 of well 1. The sand arches are formed as a resultof cohesion or capillary forces between the sand grains. The formationis stabilized as a result of the overburden stress acting on the sandgrains in the arch. The sand arches can be considered to be themechanism by which the unconsolidated formation 5 is consolidated, thusallowing fluids to be produced at a high rate therefrom withoutproducing any substantial amount of solid materials, referred to assand, from the formation. The production of fluids at a high rate fromthe unconsolidated formation 5 results in the formation of a water cone17 which cones upward from the bottom water 7 into well 1. This watercone l7 and the resulting high concentration of water associatedtherewith reduces the capillary pressures existing in the zone of theunconsolidated formation invaded by the water cone, thereby causing thefailure of the sand arches in the affected zone. The sand retainer 15controls the production of sand from the affected zone of theunconsolidated formation 5 while allowing hydrocarbons and water to beproduced from this portion of the formation into well 1. The productionof water from the water cone 17 through the sand retainer 15 tends tolimit the upward extension of water cone 17. Thus, in accordance withthis invention, said production is controlled by the sand retainer 15from that zone of the formation damaged by the water cone l7, and sandproduction is controlled by the sand arches in that portion of theformation adjacent the open production interval 12 and above the watercone 17.

In accordance with still another aspect of this invention, the sandretainer 15 is positioned in well 1 prior to any substantial disturbanceof unconsolidated formation 5 by production of fluids therefrom.Subsequently, fluids are produced from the formation at a suflicientlyhigh rate to form sand arches in the formation. Preferably, the sandarches are formed slowly around each perforation to stabilize theformation. This is done by incrementally increasing the production rateand producing at each rate until sand-free production is obtained. Thisincremental increase in the production rate is continually increasedabove the rate at which sand-free production is obtained until eitherthe flow capacity of the production tubing is reached or until formationstability is no longer attained. By forming the sand arches inaccordance with the above procedure, sudden shifts within the formationare avoided, thereby lessening the chance of the occurrence of formationfailures. In addition, the chance is lessened for a large volume of sandto be produced when the well is first put on production.

Once the well is placed on the production it is preferred that it not beshut in, in order to avoid any alterations in the stress distribution inthe formation which would subject the formation to shock and possiblycause some sand production from the hydrocarbonproducing interval beforeequilibrium is again attained. Should it become necessary to close inthe well this may be done by closing valve 33. Prior to opening valve 33it is preferred that a gas-filled surge vessel 29 be connected into theproduction line 31 to minimize shock to the formation when the formationis again put on production. The surge vessel 29 is charged with highpressure gas from a gas source 35 through pipe 37 and is connected intothe production line 31 by opening valve 39 in line 41. The high pressuregas in surge vessel 29 should be at a pressure no higher than thepressure existing in formation 5.

What is claimed is:

1. A method of producing fluids from an unconsolidated formation, saidformation being penetrated by a substantially vertical well having anopen production interval communicating with said unconsolidatedformation, comprising:

a. producing fluids from said formation into said sub stantiallyvertical well through a sand retainer located adjacent a lower portionof said 'open production interval, said sand retainer terminating at itsupper extremity at an intermediate location of said open productioninterval; and

b. concomitantly with step (a) producing fluids from said formation intosaid substantially vertical well through an upper portion of said openproduction interval above said sand retainer.

2. The method of claim 1 wherein said sand retainer is located adjacentno more than the lower percent of said open production interval.

3. The method of claim 1 wherein said sand retainer comprises a gravelpack.

4. A method of producing hydrocarbons and water contained in anunconsolidated formation, said hydrocarbons being underlain by bottomwater, said formation being penetrated by a well having an openproduction interval communicating with said unconsolidated formation,the steps comprising:

producing hydrocarbons and water from said formation into said wellthrough a sand retainer located adjacent a lower portion of said openproduction interval, said sand retainer extending from the lowerextremity of said open production interval upward to approximately theuppermost level to which a water cone will rise from said bottom water;and producing hydrocarbons from said formation into said well through anupper portion of said open production interval above said sand retainer.

5. The method of claim 4 wherein said sand retainer comprises a gravelpack.

6. The method of claim 5 wherein said gravel pack extends from the lowerextremity of said open production interval upward for no more than 75percent of said open production interval.

7. A method of producing fluids from an unconsolidated formation, saidformation being penetrated by a well having an open production intervalcommunicating with said unconsolidated formation, comprising:

a. forming a sand retainer in said well adjacent a lower portion of saidopen production interval, said sand retainer extending from the lowerextremity of said open production interval and terminating at its upperextremity at an intermediate location of said open production interval;

b. producing fluids at a first rate from said well until sand-freeproduction is attained;

c. repeating step (b) at incremental higher production rates until aproduction rate is attained at which sand-free production is no longerattained; and

d. producing fluids from said well at a production rate slightly lessthan said rate at which sand-free production is no longer attained.

8. The method of claim 7 wherein said sand retainer comprises a gravelpack.

9. The method of claim 8 wherein said gravel pack is adjacent no morethan the lower percent of said open production interval.

10. A substantially vertical well extending from the surface of theearth and penetrating an unconsolidated formation, said substantiallyvertical well having an open production interval communicating with saidunconsolidated formation and having a sand retainer located adjacent alower portion of said open production interval and terminating at itsupper extremity at an intermediate location of said open productioninterval.

11. The well of claim 10 wherein said sand retainer comprises a gravelpack.

12. The well of claim 11 wherein said gravel pack is located adjacent nomore than the lower 75 percent of said open production interval.

a a t a

1. A method of producing fluids from an unconsolidated formation, saidformation being penetrated by a substantially vertical well having anopen production interval communicating with said unconsolidatedformation, comprising: a. producing fluids from said formation into saidsubstantially vertical well through a sand retainer located adjacent alower portion of said open production interval, said sand retainerterminating at its upper extremity at an intermediate location of saidopen production interval; and b. concomitantly with step (a) producingfluids from said formation into said substantially vertical well throughan upper portion of said open production interval above said sandretainer.
 2. The method of claim 1 wherein said sand retainer is locatedadjacent no more than the lower 75 percent of said open productioninterval.
 3. The method of claim 1 wherein said sand retainer comprisesa gravel pack.
 4. A method of producing hydrocarbons and water containedin an unconsolidated formation, said hydrocarbons being underlain bybottom water, said formation being penetrated by a well having an openproduction interval communicating with said unconsolidated formation,the steps comprising: producing hydrocarbons and water from saidformation into said well through a sand retainer located adjacent alower portion of said open production interval, said sand retainerextending from the lower extremity of said open production intervalupward to approximately the uppermost level to which a water cone willrise from said bottom water; and producing hydrocarbons from saidformation into said well through an upper portion of said openproduction interval above said sand retainer.
 5. The method of claim 4wherein said sand retainer comprises a gravel pack.
 6. The method ofclaim 5 wherein said gravel pack extends from the lower extremity ofsaid open production interval upward for no more than 75 percent of saidopen production interval.
 7. A method of producing fluids from anunconsolidated formation, said formation being penetrated by a wellhaving an open production interval communicating with saidunconsolidated formation, comprising: a. forming a sand retainer in saidwell adjacent a lower portion of said open production interval, saidsand retainer extending from the lower extremity of said open productioninterval and terminating at its Upper extremity at an intermediatelocation of said open production interval; b. producing fluids at afirst rate from said well until sand-free production is attained; c.repeating step (b) at incremental higher production rates until aproduction rate is attained at which sand-free production is no longerattained; and d. producing fluids from said well at a production rateslightly less than said rate at which sand-free production is no longerattained.
 8. The method of claim 7 wherein said sand retainer comprisesa gravel pack.
 9. The method of claim 8 wherein said gravel pack isadjacent no more than the lower 75 percent of said open productioninterval.
 10. A substantially vertical well extending from the surfaceof the earth and penetrating an unconsolidated formation, saidsubstantially vertical well having an open production intervalcommunicating with said unconsolidated formation and having a sandretainer located adjacent a lower portion of said open productioninterval and terminating at its upper extremity at an intermediatelocation of said open production interval.
 11. The well of claim 10wherein said sand retainer comprises a gravel pack.
 12. The well ofclaim 11 wherein said gravel pack is located adjacent no more than thelower 75 percent of said open production interval.